Known piezoelectric devices are used as ultrasonic motors (for example, Japanese Unexamined Patent Publication No. 2008-99549 and No. 2010-219464). A piezoelectric device disclosed in each of these documents includes a body and a friction member attached to the body. Application of a voltage to the body generates a longitudinal vibration mode, and a flexural vibration mode in the body. In the former mode, the piezoelectric device oscillates in a longitudinal direction of the body. In the latter mode, the piezoelectric device oscillates in a thickness direction of the body. In accordance with this, the friction member is brought into contact with a driven body, moving in an elliptical manner and displaces the driven body by frictional force.